Knock Sensor resistance

[cambmx]

Hey, I'm new to the forum but I've been reading for a long time. I have a 1993 Legacy SS with wrx turbo and wrx intercooler, exhaust, and MBC at 9-10 psi depending on gear if that changes anything for the sensors or not I do not know.

My problem is i have severe hesitation, not all the time, but a lot of times. It will hit full boost but feel like someone is putting on the brakes, and then sometimes it just flies. totally unpredictable.

So, i heard the knock sensor could cause this, I took it off to look at it, no cracks, but it did have lots of corrosion on the block/bottom and top of sensor, and the bolt is kinda rusty. I measured resistance of just the sensor, and it was like 3 ohms, not 560k ohms, like i read somewhere it was supposed to be, but I remembered seeing that I should have checked that resistance from the ecu to the ground instead of the sensor.

sooooo, Where is the ecu? and is there a way to check the sensor when its off? (since I have it off already)

Thanks!

[Legacy777]

Welcome to the BBS.

Since you have the knock sensor removed, you need to test the resistance between the pin on the knock sensor connector and the metal part of the sensor that makes contact with the engine. This is what should be 560k ohms.

Here's the diagnostic info from the factory manual if you don't already have it.
http://www.main.experiencetherave.com/s ... r_diag.pdf

I'd also suggest checking the knock sensor wire on the chassis side from the connector in the engine bay to the ECU pin. It should be near 0 ohms.

The ECU is up under the dash, left of the steering colum. Here's a picture.

http://www.main.experiencetherave.com/s ... cuhide.jpg

If you have any questions, let us know.

[cambmx]

thanks for the fast reply!! ok, I tested that, and thats got only 3 ohms, which seems pretty far away from 560k haha! at first I thought i may be measuring it wrong, but I double and triple checked it and It still 3. so I should replace the sensor, and then go from there?

and is it possible that this would not throw a CEL for knock sensor? Its throwing one for the O2 sensor, but thats the only code.

[Legacy777]

If you're reading 3 ohms, then yes I'd suggest replacing the sensor.

I don't know about the CEL....these cars are kind of weird. When I did my aftermarket ECU upgrade I had noticed my knock sensor wire was bad and wasn't making any connection to the ECU. However I don't know if that happen when I did the work to put the ECU in or before. I had no CEL prior....so who knows.

[cambmx]

so knock sensor in, but then the car ran still really bad, though no knocking or pinging, so I know that the sensor is finally working! I'm looking into the fuel pump, cause I checked the plugs and they were reallyu white, and it felt like it was way way lean, wouldnt even let me hit 0 lbs on the boost gauge, it felt like i was slammin on the brakes from like 2 psi vacuum.?!?! hopefully i can find the fuel pump not working

[Jessekrs123]

so knock sensor in, but then the car ran still really bad, though no knocking or pinging, so I know that the sensor is finally working! I'm looking into the fuel pump, cause I checked the plugs and they were reallyu white, and it felt like it was way way lean, wouldnt even let me hit 0 lbs on the boost gauge, it felt like i was slammin on the brakes from like 2 psi vacuum.?!?! hopefully i can find the fuel pump not working

Do you have any supporting mods like for fuel? Walbro 255 or bigger injectors? I'd get a wideband to monitor your AFRs. If your plugs are white, there is not enough fuel.

[cambmx]

no, I do not have other mods, I ended up finding out I had full power to the fuel pump, But I had one lying around that I had bought a long time ago to put in and never did, so I threw it in, and wow!!! its so smooth, and so fast!!!! we had a lot of snow last night, so I cant tell how hard exactly its pulling, but I found one spot in an intersection that was plowed a lot, and it hooked up and just ripped me into my seat

now some questions:

Should I be doing fuel mods? its at stock levels of boost I thought, or near stock..

could I crank the boost up more with the mods I have? (02 wrx intercoller, wrx turbo, aftermarket header, downpipe, and catback)

and what do you suggest as a wideband?

Thanks!

[Legacy777]

You can most likely bump the boost just a little so it stays under fuel cut. It's not going to be a big jump, but may help a little. I would not suggest doing that until you have a wide band though.

The catch with these cars is that all the components, injectors, MAF, etc are pretty much at the limit. So adding one thing to get more power causes a domino effect and you need to upgrade other stuff, and then the biggest sticking issue is the ECU.

As for a wide band, I'd suggest Innovative or Zeitronix.